Laser/EDM drilling manufacturing cell

ABSTRACT

A process and apparatus for drilling precision small diameter holes in fuel nozzle parts includes the process of directing a laser beam against the nozzle part at a first hole drilling station to form an undersized hole therethrough and thereafter positioning the nozzle part with the laser hole formed therethrough in alignment with a wire electrode of an electrical discharge machine and controlling the energy input to the electrode wire and advancing it with respect to the preformed laser hole so as to form a precision hole diameter and surface finish throughout the length of the laser beam formed hole as EDM particles are flushed through a flow path defined by the laser hole from one face to the opposite face of a part wall.

This is a continuation, of application Ser. No. 060,826, filed on June12, 1987, Abandoned.

TECHNICAL FIELD

The present invention relates generally to precision drilling systems,and more particularly to a combined laser and electrical dischargemachining cell for forming precision small diameter holes in nozzleparts.

BACKGROUND ART

U.S. Pat. No. 4,504,727 sets forth a laser drilling system whichutilizes photoacoustic feedback to monitor and control the laser beam soas to control a laser drilling process. In the -727 patent, the drillingprocess is provided to produce an array of holes in a multilayeredprinted circuit board. In such arrangements, it is necessary to closelycontrol the pulse power of a laser so that it can be adjusted for eachsuccessive layer in such structures. There is no suggestion in the -727patent that the laser formed hole be later precision finished to a closetolerance suitable for use in precision small diameter holes in nozzleparts for fuel injection systems or the like.

U.S. Pat. No. 3,696,504, issued Oct. 10, 1972, discloses a processwherein a laser beam is used to form a hole through a part. In the caseof metal parts, it is recognized that such laser formed holes can effectthe metallurgy of the parts. In accordance with the process of the -504patent, the altered metallurgy of the laser formed hole is subsequentlymachined away by a mechanical tool having a blade which reams the wallof the laser formed hole.

When drilling precision small diameter holes for diesel engine fuelsystem nozzles, it is critical that the spray holes formed in the nozzlehave precise diameters and a smooth internal microfinish to producedesired flow rates and angle accuracy of fuel discharge into enginecombustion chambers.

In the present invention, undersized holes are first formed by a laserto reduce the cycle time for penetration of the hole through the part.The part is then finished by electrical discharge machining.Specifically, a wire electrode of an electrical discharge machine isadvanced through the previously laser formed undersized hole which issized to provide an annular flow path for unidirectional flow ofelectrolyte during an EDM process. The flow path is sized so thatparticles produced during the EDM process will be flushed from the partby the unidirectional flow of electrolyte. The wire electrode is sizedand is connected to a pulse generator to control energy at a spark gapbetween the wire electrode and a grounded workpiece so as to form a holeof precision dimension and with a microfinished surface thereon. The useof a laser to form a rough undersized hole, followed by a precisionfinishing of the laser hole by electrically discharge machining theinner surface thereof reduces the total hole forming cycle time ascompared to the cycle time of prior computer controlled EDM holedrilling equipment. Furthermore, the combination of laser drilling ofundersized holes and EDM finishing enables nozzle parts to be producedat high production rates while maintaining hole size precision andfinish.

SUMMARY OF THE INVENTION

The manufacturing cell of this invention has platform means for locatingnozzle parts for programmed, sequentially accurate part transfer betweena laser drilling station and an EDM finishing station. The laserdrilling station includes a laser head; a microprocessor control and abeam delivery system. A CNC controlled multi-axis drive will accuratelylocate the indexing table to produce a variety of holes in a nozzle partwhen it is indexed with respect to the laser drilling station and EDMstation. The cell includes a shield station with a plunger formed frompolytetrafluoroethylene (PTFE) and retracting feeder mechanism to shieldthe inside surface of the nozzle part during the impingement of thelaser beam thereon to form an undersized hole therethrough which createsa path for flow of EDM electrolyte and a path to flush particles fromthe part during EDM precision finishing of the laser hole. The PTFEplunger and retractor feed mechanism are removed from the nozzle partand the part is precision indexed to the EDM station where a wireelectrode is used to finish the undersized laser hole. An adaptivecontrol power supply selectively applies an electrical dischargemachining current across a gap between the wire electrode and the wallof the laser hole. The EDM controller advances the wire electrode withrespect to the laser hole as EDMed particles are flushed therethrough soas to form a precision hole having a right cylindrical configuration anda microfinish on the inner surface of the laser hole. The aforedescribeddual drilling process reduces the hole drill and finish cycle time. Theprocess improves hole diameter and cylinder shape precision and alsoimproves smoothness of internal hole surfaces so as to assure closelycontrolled flow rates and angle accuracy of fuel exiting from such fuelnozzles.

The main object of the invention is to produce a hole in a fuel nozzlepart by the use of dual drilling steps including a first laser beam holedrilling step and precision EDM drilling of the laser hole to accuratelysize and finish the inside surfaces of an undersized laser formed holeto produce a resultant hole with a precise cylindrical configurationthereby to improve flow rate and flow exit patterns of fluid flowtherethrough.

Another object of the present invention is to provide such a duallaser/EDM process for precision nozzle hole formation wherein theundersized laser drilled hole therethrough is preformed to define a holefor receiving an EDM electrode and to define a path for flushing EDMparticles from the part without flow reversal of the electrolyte and theerosion particles carried thereby.

Other objects, features and advantages of the present invention willbecome more apparent from the following description take in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view of a combination laser and EDM holedrilling manufacturing cell of the present invention;

FIG. 2 is an enlarged view of a fuel nozzle tip shown in alignment withlaser and EDM heads;

FIG. 3 is a sectional view of a prior art nozzle having the hole formedtherein solely by use of an EDM electrode and electrical dischargemachining processing;

FIGS. 4A-4C are enlarged fragmentary perspective views of a part drilledby a combination laser and EDM process; and

FIG. 5 is an elevational view of an insert for shielding a nozzle partduring the laser hole drilling step of the method of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, a laser hole drilling station 10 isillustrated. It includes a laser head 12 for producing a laser outputbeam 14. Station 10 is angularly offset with respect to an EDM holedrilling station 16 having an EDM head 18.

FIG. 5 shows a shield station 20 including a plunger feed and retractingmechanism 22 which positions a protective plunger insert 23 configuredto cover the interior surface 24 of a nozzle workpiece 25 to shield itwhen a laser beam breaks through the workpiece wall during a laserdrilling step to be described. The nozzle workpiece 25 is illustrativeof the type of precision fluid flow device whose performance can beenhanced by practicing the method of the present invention. Theinvention is equally suitable for use in the manufacture of otherdevices or parts which require precisely shaped hole configurationsformed therethrough.

In the machine cell of FIG. 1, the nozzle workpiece is supported by anindexing platform 26 for movement with respect to the various workstations. The indexing platform 26 more particularly includes a carriage27 connected to a drive motor 28 and suitable drive gear means 30 todrive carriage 27 into a plurality of vertically displaced locations tolocate the nozzle workpiece 25 at the work stations. The workpiece 25 islocated on a rotatable plate 32 on the platform 26. The plate 32 isdriven by an actuator 34 to position it in a plurality of hole formingindexed positions. Cross-slide 36 supports the platform 26. It is drivenby motor 38 and drive gear 40 to position the workpiece 25 at the laserhead 12 and the EDM head 18.

The EDM drilling station 16 includes a base 44 with a carriage 46 forfeeding a wire electrode 48 for finish machining undersized laserdrilled holes in the nozzle during a precision machining operation ofthe hole drilling system 10. Specifically, the wire electrode passesthrough a refeed mechanism 50 and a wire guide 52 to the nozzleworkpiece 24. The refeed mechanism 50 is adapted to advance theelectrode wire relative to the carriage 46 upon retraction of thecarriage after each machining operation.

An operating sequence of the cell includes moving the carriage 27 to thelaser hole drilling station 12 and to the EDM hole drilling station 16.The machine is controlled by a CNC controller 53 at each such station toposition the nozzle workpiece 25 in a preprogrammed sequence at eachstation to form a desired series of precision microfinished holestherein.

FIG. 3 shows the shape of a nozzle hole formed solely by use of an EDMhole drilling process. During such a process a wire electrode connectedto a suitable power generator of the type set forth in U.S. Pat. No.4,361,745 issued Nov. 30, 1982 to Rupert et al for Process Control forElectrical Discharge Machining Apparatus is advanced with respect to aworkpiece to cause a somewhat conoidally shaped hole 54 to be formeduntil the electrode breaks through the part wall. During the electricaldischarge machining of the hole, the electrode is eroded to have atapered end 56 and at the end of the hole formation stroke the taperedend 56 will produce a breakout edge 58 that will require a furtherstroke of the electrode to complete the hole. Furthermore, before theelectrode end 56 breaks through the part wall, the electrolyte reverseflows around the electrode. Consequently, particles which are erodedfrom the part by the electrode are backflushed from the part through thespark gap region 59. Such a reverse flow pattern of eroded particles cancause the walls of the holes to be formed slightly off-center and resultin a hole that is not of a precise right cylindrical configuration.

In the present invention, such problems are obviated. Hence, as shown inFIGS. 4A-4C, the workpiece 25 is positioned so that its tip 61 isaligned with the output beam 14 from the laser head 12. The laser is aNd-YAG laser which is of the type set forth in U.S. Ser. No. 621,342filed June 18, 1984 and owned by the present assignee.

The laser head 12 is pulsed at a power output level which will producean undersized laser hole 60 in the nozzle tip 61. In order to meet thefinal desired nozzle hole specifications, a wall thickness 62 must beremoved. Such removal is accomplished by steps including indexing thelaser hole into alignment with the EDM hole drilling station 16. Theelectrode 48 is then advanced into the hole 60. As illustrated in FIG.4B, the electrode diameter is selected to define a spark gap to erodethe wall thickness 62. The diameter is further selected so as to definean annular electrolyte flow path 64 through which the electrolyte flowsin a unidirectional path without flow reversal during the EDM erosionprocess. As a consequence, erosion particles from the part are carriedaway from the advancing electrode at the spark gap formed between theelectrode tip and the nozzle. The preformed laser hole 60 thereby servesto define a lead-in path which will prevent or substantially reduce theend taper on the electrode as it advances through the hole. Further,flushed erosion products will not interfere with the hole formationprocess. The result is a truly accurately formed right cylindrical holeshape. Such hole shapes will result in desired flow meteringcharacteristics. Further, they will produce more predictable flow exitpatterns from nozzles made by use of the method of the presentinvention.

After each EDM operation, the downward limit of the carriage 46 issensed by a limit switch 66 which causes plate 32 to be indexed to placethe next laser drilled hole at the EDM work station where the wire isdirected form the wire guide 52. When the plate 32 is indexed to theposition for machining the last laser drilled hole in the nozzleworkpiece 25, a limit switch 68 conditions the machine to actuate thedrive motors 28, 30 to transfer the nozzle 25 to a flow test station 70.The test station or flow test station 70 includes a stand 72 having anest 74 therein to receive the nozzle workpiece 25. An air gauge testhead 76 is located in overlying relationship to the stand 72 and isadapted to operatively engage the nozzle 25 to measure the air flowcapacity thereof. After the testing operation is completed, the nozzleworkpiece 25 is transferred from the flow test station 70 to a partunloading station where the part is either accepted or rejected by aknown selection process which is based upon the flow result that isobtained at the flow test station 70. Representative flow testingstations and sorting stations for accomplishing such selection ofdesired workpieces are set forth in copending United States Application781,115 entitled, "Method and Apparatus for Electric DischargeMachining", owned by the present assignee.

Although the description of this invention has been given with referenceto a particular embodiment, it is not to be construed in a limitingsense. Many variations and modifications will be apparent to thoseskilled in the art. For a definition of the invention, reference is madeto the appended claims.

What is claimed is:
 1. In a dual drilling process for forming a finishedprecision hole through a part having a wall with an inside surfacedefining an internal cavity, the improvement comprising:high speed laserdrilling the wall by focusing a beam of laser energy on an imperforatesegment of the wall to form an undersized hole of irregular form throughthe wall from the exterior thereof to the internal cavity whilemaintaining the internal cavity under ambient pressure conditions;shielding the surface of the internal cavity to prevent erosion thereofduring the laser drilling step; removing the shielding and sequentiallyaligning an electrode with respect to the undersized hole and applyingcurrent between the electrode and the wall of the undersized hole tospark erode a predetermined thickness of the wall at the previouslylaser formed undersized hole to shape the irregularly formed undersizedhole as a right cylindrical passage from the interior surface to theexterior surface of the wall.
 2. In apparatus for drilling precisionsmall diameter holes in a part having a wall and an interior cavitybounded by the wall, the improvement comprising:machine base means;laser means and electrical discharge machining means on said machinebase means; means for locating the wall sequentially first with respectto said laser means and then with respect to said electrical dischargemachining means; means for controlling said laser means to focus a beamof laser energy on an imperforate segment of the wall part to form anundersized hole of irregular form through the wall from the exteriorthereof to the internal cavity while maintaining the internal cavityunder ambient pressure conditions; means for shielding the surface ofthe internal cavity to prevent erosion thereof during the laser drillingstep; and means for removing the shielding and sequentially aligning anelectrode with respect to the undersized hole and applying currentbetween the electrode and the wall of the undersized hole to spark erodea predetermined thickness of the wall at the previously laser formedundersized hole to shape the irregularly formed undersized hole as aright cylindrical passage from the interior surface to the exteriorsurface of the wall.
 3. In the process of claim 2, electrical sparkmachining the undersized hole by the steps of selecting an electrode ofright circular cross-section of a diameter less than the undersized holeand of a length greater than that of the undersized hole andprogressively feeding the electrode from the exterior end of theundersized hole to the interior end thereof while applying currentbetween the electrode and the wall to progressively shape theirregularly formed hole as a right cylindrical passage from the exteriorsurface to the interior surface of the wall.
 4. In the process of claim3, selecting an annular space between the electrode and the wall of theundersized hole dimensioned to define a continuously progressivelyadvancing annular axial passage from the exterior surface to theinterior surface of the wall for uniformly constant flow of electrolytethrough the wall for flushing spark erosion particles from theirregularly formed undersized hole as the electrode progressivelyadvances therein so as to produce a precise right cylindrical passagethrough the wall.
 5. In the apparatus of claim 2, said laser meansincluding a laser head and said electrical discharge means including awire feed head; said laser head and said wire feed head being located ina common plane and being angularly spaced with respect to one another.6. In the process of claim 1, progressively feeding a wire electrodehaving a diameter less than that of the undersized hole through theundersized hole for shaping the irregular form thereof to a constantdiameter right cylindrical passage from the exterior surface to theinterior surface of the wall.
 7. In a dual drilling process for forminga finished precision hole through a part having a wall with an insidesurface defining an internal cavity, the improvement comprising:highspeed laser drilling the wall by focusing a beam of laser energy on animperforate segment of the wall to form an undersized hole of irregularform through the wall from the exterior thereof to the internal cavitywhile maintaining the internal cavity under ambient pressure conditions;shielding the surface of the internal cavity to prevent erosion thereofduring the laser drilling step; removing the shielding and sequentiallyaligning an electrode with respect to the undersized hole and applyingcurrent between the electrode and the wall of the undersized hole tospark erode a predetermined thickness of the wall at the previouslylaser formed undersized hole to shape the irregularly formed undersizedhole as a precision hole from the interior surface to the exteriorsurface of the wall.
 8. In apparatus for drilling precision smalldiameter holes in a part having a wall and an interior cavity bounded bythe wall, the improvement comprising:machine base means; laser means andelectrical discharge machining means on said machine base means; meansfor locating the wall sequentially first with respect to said lasermeans and then with respect to said electrical discharge machiningmeans; means for controlling said laser means to focus a beam of laserenergy on an imperforate segment of the wall part to form an undersizedhole of irregular form through the wall from the exterior thereof to theinternal cavity while maintaining the internal cavity under ambientpressure conditions; means for shielding the surface of the internalcavity to prevent erosion thereof during the laser drilling step; andmeans for removing the shielding and sequentially aligning an electrodetip with respect to the undersized hole and applying current between theelectrode and the wall of the undersized hole to spark erode apredetermined thickness of the wall at the previously laser formedundersized hole to shape the irregularly formed undersized hole as aprecision hole from the interior surface to the exterior surface of thewall.
 9. In a dual drilling process for forming a finished precisionhole through a wall with an imperforate segment and two surfaces, theimprovement comprising:high speed laser drilling the wall by focusing abeam of laser energy on the imperforate segment of the wall to form anundersized hole of irregular form through the wall while maintaining thewall surfaces under ambient pressure conditions; aligning an electrodetip with respect to the undersized hole following laser drilling thereofand applying current between the electrode tip and the wall at theundersized hole and advancing the electrode toward the wall to sparkerode a predetermined thickness of the wall at the previously laserformed undersized hole to shape the irregularly formed undersized holeas a precision hole through the wall.
 10. In apparatus for drillingprecision small diameter holes in a part having a wall with two surface,the improvement comprising:machine base means; laser means andelectrical discharge machining means on said machine base means; meansfor locating the wall sequentially first with respect to said lasermeans and then with respect to said electrical discharge machiningmeans; means for controlling said laser means to focus a beam of laserenergy on an imperforate segment of the wall part to form an undersizedhole of irregular form through the wall while maintaining the twosurfaces of the wall at ambient pressure conditions; an electrode insaid electrical discharge machining means; means for sequentiallyaligning said electrode with respect to the undersized hole and applyingcurrent between the electrode and the wall at the undersized hole tospark erode a predetermined portion of the wall at the previously laserformed undersized hole therein to shape the irregularly formedundersized hole as a precision hole through the wall.